Belt grinding assemblies are known that are adapted for use to grind a smooth arc on an edge surface extending between major side surfaces on an object or elongate bar such as a wrench, which edge surface has a predetermined shape when viewed in the planes of the major surfaces that may or may not be linear along the length of the wrench. Such grinding assemblies are useful to change an original rough or irregular edge surface resulting from the method by which the wrench was formed (e.g., drop forging) into a smoothly arced edge surface that is more aesthetically pleasing and easier on the hand of user of the wrench than the original rough or irregular edge surface. One such grinding assembly comprises the combination of (1) a belt grinding assembly including a drive mechanism for driving an abrasive belt in a first direction along a path past a backup platen fixed to frame means for the assembly, which platen has a support surface for the abrasive belt adjacent its rear surface that is straight in direction of travel of the belt and has a uniform shape corresponding to the shape of the edge surface to be radiused in a direction at a right angle to the direction of travel of the belt; and (2) bar manipulating means for moving the edge surface of the bar along an arcuate path about an axis at a right angle to the direction of travel of the belt into forceful engagement with the abrasive coated surface of the belt along the support surface to form the radius on the bar.
In this known belt grinding assembly the bar manipulating means is provided by a conveyor including a conveyor belt formed by two parallel spaced endless lengths of roller chain, metal slats extending transversely between opposite chain links, and receptacles for the bars attached to the slats on the sides of the slats opposite the lengths of chain; and a drive mechanism for the belt including two parallel spaced axles each carrying two axially spaced sprockets around which the chains were tensioned. Each of the receptacles is adapted to receive one of the bars therein with the length of the bar extending parallel to the slats and an edge surface of the bar projecting away from the slats, and the sprockets at one end of the conveyor are positioned so that movement of one of the receptacles around the sprockets on one of the axles will move a bar in the receptacle in an arc into forceful engagement with the abrasive belt along the support surface to grind a radius on the edge surface of the bar.
Another such grinding assembly comprises the combination of (1) a belt grinding assembly including a drive mechanism for driving an abrasive belt in a first direction along a path past a grinding station; and (2) bar manipulating means for moving the edge surface of the bar along an arcuate path about an axis at a right angle to the direction of travel of the belt into forceful engagement with the abrasive coated surface of the belt at the grinding station to form the radius on the bar; the bar manipulating means being provided by a drum having receptacles for the bars attached to its periphery; and a chain drive mechanism for the drum. Each of the receptacles is adapted to receive one of the bars therein with the length of the bar extending parallel to the axis of the drum and an edge surface of the bar projecting away from the slats, and the drum is positioned so that movement of one of the receptacles around its periphery will move a bar in the receptacle in an arc into forceful engagement with the abrasive belt along the support surface to grind a radius on the edge surface of the bar.
While such grinding assemblies can grind a radius on the side surface of a bar or wrench, they present several problems. Looseness of the bar in the holder, between the conveyor belt and the sprockets, or in the chain drive allows the bar to momentarily not be moved by the drive mechanism as the bar is initially brought into engagement with the abrasive belt along the support surface, after which the drive mechanism does move the bar into forceful engagement with the abrasive belt until the bar is positioned along the support surface so that the force of such engagement is directed to move the bar with the belt, whereupon such looseness allows the bar to move with the belt, resulting in movement of the bar too quickly out of engagement with the abrasive belt along the support surface. The result of such engagement between the bar and the belt is to produce a ground edge surface on the bar that is not uniform in that too much metal is removed from the portion of the bar that initially engages the belt, and too little metal is removed from the portion of the bar that is in final engagement with the belt. Also, the bar or wrench can fall free of the holders as it moves out of engagement with the belt, which can be dangerous.
A problem associated with the grinding assemblies described in U.S. application Ser. No. 07/359,729, filed May 31, 1989 or EPO Patent Application 0400901 is that such grinding assemblies tend to have difficulty in grinding small arcs (e.g. less than 1.0 inch radius on 0.25 inch thick edges of wrenches) on objects. For such a grinding assembly, the wheel should have a sufficiently large radius so that a number of tool receptacles may be placed on the periphery of the wheel. Generally, the larger the radius of the wheel, the greater the number of tool receptacles may be placed on the periphery of the wheel and the slower the speed of the periphery of the wheel per the number of objects ground. However, as the radius of the wheel increases, the arc in which the receptacles move the workpieces into forceful engagement with the abrasive belt along the support surface becomes "flatter". The resultant radius ground on the object is relatively large and thus, such devices tend to grind an undesirably large radius on the edge surface of the wrench or workpiece which results in a wrench with an insufficiently smooth edge which may be rough on the hands of a user and less aesthetically pleasing.